What happened is this: The bible explicitly states that you cannot know the time of the second coming. These guys actually got it right. If God had left it like that, he would have looked like an idiot, because they figured out his secret plan.

According to a strict interpretation of the Book of Deuteronomy, Harold Camping should be put to death.

20 But a prophet who presumes to speak in my name anything I have not commanded, or a prophet who speaks in the name of other gods, is to be put to death."

21 You may say to yourselves, "How can we know when a message has not been spoken by the Lord?" 22 If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously, so do not be alarmed.Deuteronomy 18:20-22